Three functionalized derivatives of tetraphenylethylene (TPE), namely, 1,2-bis(4-methoxyphenyl)-1,2-diphenylethene (<b>1</b>), 1,2-bis(4-hydroxyphenyl)-1,2-diphenylethene (<b>2</b>), and 1,2-bis[4-(3-sulfonatopropoxyl)phenyl]-1,2-diphenylethene sodium salt (<b>3</b>), were synthesized and their fluorescence properties were
investigated. All the TPE molecules are nonluminescent in the solution state but are induced to emit efficiently
by aggregate formation. This novel process of aggregation-induced emission (AIE) is rationalized to be caused
by the restriction of intramolecular rotations of the dye molecules in the aggregate state. The possibility of
utilizing the AIE effect for protein detection and quantification is explored using bovine serum albumin (BSA)
as a model protein, with salt <b>3</b> being found to perform as a stable, sensitive, and selective bioprobe.